Considering current forecasts that petroleum sources will be exhausted within the next decades, other energy sources have been researched worldwide. Among these alternatives, biofuels, such as ethanol and biodiesel, present a significant potential, since they are low pollutant and also renewable energy forms.
In the specific case of biodiesel, for large scale production, technologies have been developed from raw materials rich in lipids and fatty acids of plant and animal origin. Unfortunately, lipids and fats derived from plants and animals as produced worldwide only meet the demand for the consumption for food production and oleochemical industries. Therefore, it is extremely important to search for other alternative sources for the production of lipids and fatty acids for use in the production of biodiesel and fuel oil. The microbial synthesis of lipids and fats is a technological alternative for this purpose.
There are three main advantages in lipid production by microorganisms. First, generation is very quick, i.e. the microbial biomass doubles in an interval of hours, yeasts produce a new generation between one and three hours, algae between two and six hours and fungi between four and twelve hours. Second, less production area is required for one single mass of fat material, i.e. it is possible to produce in a fermentor the same quantity of lipids in much less time and in an area up to thirty times smaller than used to plant vegetables. And third, it is possible to better control the production process and the product, i.e. bioreactor, or fermentor, control is much simpler than the control of agricultural production, besides not depending on climate and/or season variations.
Not all microorganisms accumulate lipids in enough quantity to make their economic and industrial production become viable. Microorganisms considered as oil producers are those that can accumulate more than 20% lipids within their dry biomass. Basics of physiology to accumulate lipids by microorganisms have been studied by various researchers worldwide.
Yeasts may be mentioned as one of the most interesting groups of microorganisms, for their ability to accumulate large quantities of lipids intracellularly, as well as for their relatively high rates of growth and their similarity in triglyceride composition with vegetal oils.
In some cases, said microorganisms may accumulate up to 70% of their dry weight in lipids, and the main formed triglycerides have chains between 16 and 18 atoms of carbon.
During the Second World War, due to scarce vegetal lipids, the cultivation of yeasts enabled the manufacture of oils and their derivatives, such as margarines and other products. In the current cosmetic industry, fatty acids with high commercial value are used as emulsifiers and stabilizers. Said lipids may equally be synthesized by microbial route.
Algae represent another important source of lipids and are equally able to accumulate concentrations of up to 65% over the weight of their dry biomass. They may be classified as photosynthetic organisms, such as plants, since they use solar energy, jointly with water and carbon dioxide, to generate biomass. Within said classification, the present invention also has the purpose to make use of photosynthetic organisms growing in water environment, i.e. macroalgae, microalgae and other water organisms for the production of commercially interesting products, particularly lipids for the production of biodiesel and fuel oil.
Macroalgae are quickly growing plants reaching considerable sizes, about 50 m long. On the other hand, microalgae, as their name suggests, are microscopic photosynthetic organisms found in marine and fresh water environments.
The study of microalgae is still relatively unknown and algae as a whole still are a very little understood and used organism, biotechnologically speaking. Microalgae are divided into a series of classes, according to their pigments, life cycle and basic cell structure. The four most important classes of microalgae in terms of abundance are Bacillariophyceae, Chlorophyceae, Cyanophyceae and Chrysophyceae. They are the most primitive forms of plants, have similar photosynthetic mechanisms to higher plants, but convert solar energy into more efficient forms, due to their simple cell structure. Furthermore, since cells grow in water suspension, they have more access to water, carbon dioxide and other nutrients. For these reasons, microalgae are able to produce thirty or more times the quantity of oil per unit of planted area, in comparison to oilseeds.
We can state, therefore, that microalgae form a heterogeneous group, including photosynthesizer microorganisms, both eukaryotic and prokaryotic. Microalgae are usually unicell, gram-negative and predominantly live in water environment.
The high photosynthetic efficiency of said microorganisms make them form the base of the food chain in water ecosystems, being responsible for about 40-50% carbon fixing and oxygen production on the planet. Furthermore, microalgae synthesize organic matter from inorganic substances, such as salts, carbon dioxide and water.
From that knowledge, the microbial production of lipids appears as a viable and innovative alternative in the competition with the production of vegetal and/or animal oils and fats. Microorganisms, as simpler living beings than plants and animals, may be economically used in large or small scale for the production of biodiesel or to generate energetic fuels, as well as to generate other products.